Integrating Surface-Based Geophysics into Landslide Investigations along Highways

Characterizing active landslides is a significant challenge for geotechnical engineers and geologists, as issues of access, instability, and soft soils can impact the ability of heavy equipment to reach critical locations. Surface-based geophysical methods can be an important tool in these investigations, as they can be deployed quickly by a small team without the use of heavy equipment. In addition, surface-based geophysics can provide two- or three-dimensional profiles of the subsurface that can provide detailed information on stratigraphy and assist with locating critical layers. When used as part of an integrated site characterization effort, geophysical methods can be used to extrapolate results from limited borings or in situ tests and identify problem areas that may require additional investigation. This paper presents results from both electrical and seismic geophysical surveys at two active landslides in Alabama. Both landslides occurred along active roadways and issues with utilities and topography made investigating the slides challenging. The geophysical results were able to identify the likely failure plane at each site, which was confirmed through comparison with inclinometer and boring data. Identifying this failure zone would have been difficult if not impossible to do from either the resistivity or the seismic results alone, but integrating the results from these two methods allowed the zone to be identified. This integrated characterization approach provides a more reliable ground model for analyses and design of repairs. Challenges, such as irregular terrain and accounting for topography, encountered on these deployments, along with recommendations for future studies are discussed.